1. Field of the Invention
The present invention generally relates to a pixel structure, in particular, to a pixel structure having multiple channel areas.
2. Description of Related Art
Currently, thin film transistor liquid crystal displays (TFT-LCDs) have become a mainstream display among various flat panel displays. The TFT-LCDs may be classified into amorphous silicon TFT-LCDs and low-temperature polysilicon thin film transistor (LTPS-TFT) LCDs depending on the different materials of the channel layer.
Since the electron mobility of the LTPS-TFT may reach 200 cm2/V-sec or more, the TFT device may be made to have a smaller area so as to meet the requirement of high aperture ratio, further to increase the display brightness of the display and reduce the overall power consumption. Comparatively, the LTPS-TFT also has a high leakage current (about 10−9 μA), and a hot carrier effect may be easily induced at the drain to degrade the device. Therefore, recently, a light doped drain (LDD) is usually disposed between the channel area and the source/drain in the LTPS-TFT or a multi-channel area design is used to avoid the above problems.
FIG. 1 shows a pixel structure of a conventional polysilicon TFT-LCD. Referring to FIG. 1, the pixel structure 100 includes a scan line 110, a data line 120, a polysilicon layer 130, and a transparent pixel electrode 140. The scan line 110 has at least one L-shaped branch 112, and the polysilicon layer 130 intersects with the L-shaped branch 112 to form a first channel area 132 and a second channel area 134. Moreover, a low-temperature polysilicon layer 130 is provided with a source area 136 and a drain area 138 at its two ends, so as to form a multi-channel polysilicon TFT 150. The data line 120 is electrically connected with the source area 136, and the transparent pixel electrode 140 is electrically connected with the drain area 138. Moreover, the overlapping portion of the polysilicon layer 130 and the pixel electrode 140 further forms a storage capacitor 152. Due to the multi-channel design, the LTPS-TFT 150 staying in the turn-off state has a low leakage current, which helps to improve the performance of the pixel structure 100. However, the arrangement of the L-shaped branch 112 influences the location of the storage capacitor 152 and reduces the display aperture ratio of the pixel structure 100.